Process for the pretreatment of plastic for the purpose of adhesive metallization

ABSTRACT

THERE IS PROVIDED A PROCESS FOR THE ADHESIVE METALLIZATION OF PLASTIC SURFACES INCLUDING A CHROMOSULFURIC ETCH AND SUBSEQUENT CHEMICAL METALLIZATION AND ELECTROPLATING AND IMPROVEMENT IN WHICH THE PLASTIC SAMPLE, AFTER THE CHROMOSULFURIC ACID ETCHING, IS PREFERABLY TREATED IN AN AQUEOUS ALKALINE INTERMEDIATE BATH CONTAINING AMMONIA OR A MATERIAL HAVING, PRIMARY, SECONDARY OR TERTIARY AMINO GROUPS AND/OR CONTAINING A QUATERNARY AMMONIUM COMPOUND.

United States Patent U.S. Cl. 204-30 4 Claims ABSTRACT OF THE DISCLOSURE There is provided a process for the adhesive metallization of plastic surfaces including a chromosulfuric etch and subsequent chemical metallization and electroplating and improvement in which the plastic sample, after the chromosulfuric acid etching, is preferably treated in an aqueous alkaline intermediate bath containing ammonia or a material having, primary, secondary or tertiary amino groups and/or containing a quaternary ammonium compound.

The process of the invention is concerned with the pretreatment of plastic surfaces for the purpose of subsequent adhesive chemicogalvanic metallization.

In order to prepare plastics with a metal skin covering, there are used in an increasing degree, chemicogalvanic procedures. These comprise a series of process steps to which belong primarily the sensitization of the plastic, mostly with SnCl solution, the concurring activation with a noble metal solution, mostly with silver nitrate or palladium chloride solution and the chemicogalvanic deposition of a thin metal skin besides its electroplating and improvement.

The usability of such metallized plastic parts is determined, however, in large measure on the adhesion of the metal layer to the plastic. This depends largely on the roughness of the plastic layer. Besides the original customary mechanical roughening methods for several special types of plastics, as for example, ABS plastic (acrylonitrile-butadiene-styrene polymer) chemical process have also become known which lead to a very firm fastening of the metal film. For the most part, this purpose is served by an etching which is built up of sulfuric acid, chromic acid and usually also phosphoric acid. Through such etching, the plastic surface ingredients of the plastic are selectively dissolved, whereby a very fine network of pores and channels arise, in which the metallization solution is able to penetrate and lead to a rootlike fastening of the metal layers.

Processes have already been proposed which rest upon the proposition that by the pretreatment small particles of filler are dissolved out of the previously prepared plastic and, in this manner, provide fastening places for the metal layer. In an advantageous manner such plastic types are able to be chemicogalvanically metallized also without the use of sensitization baths, since the specially selected small filler particles make it possible to accept the roll of sensitization, while the noble metal ions of the activation solution chemically bind to it. This successful activation process without sensitization can be advantageously strengthened if the activator ions chemically bonded to the filler particles in the plastic are developed in a bath containing a reducing agent.

It has now been proven that these processes sutler under large qualitative fluctuations because a series of disturbing factors are introduced into the operation of the process through the pretreatment of the plastic part with chromosulfuric acid for the purpose of hydrophilization and roughening of the plastic surface. Frequently these processes lead only to unsatisfactory adhesiveness despite good roughening as can be detected through electronic optical investigations of the plastic surface. The basis for this is that exactly at the spot where the securing of the metal film should serve, the material remaining behind from the etching inhibits the deposition of metal. The plastic becomes covered only superficially in spite of good roughening and, therefore, adhesion is bad. Also rinsing processes, with bisulfite, as are recommended occasionally to decontamiuate the etched plastic parts, are not able to totally remove these disturbing factors. The disturbance susceptibility of the process can be reduced somewhat when one introduces very intensive intermediate rinsing processes with deionized water, which, however, has a very disadvantageous effect on the economy of the process, since it considerably lengthens the process operation.

According to the process of the present invention, these disturbances can be completely eliminated if the decontamination of the etched plastic parts are taken up with a preferably aqueous, alkaline solution containing a material having primary, secondary, or tertiary amine groups or ammonia or quaternary ammonium bases, which on the one hand functions as a strong neutralizing agent, and on the other hand binds inhibiting metal ions which come from the etching, in the form of complexes which can be removed.

Especially suitable are sodium alkaline solutions of primary and secondary aliphatic amines having one or several amine groups which are able to build very stable complexes with metal ions. Of the latter, the most outstanding is the sodium alkaline solution of ethylene diamine for decontamination of the etched plastic surfaces. The detoxification solution can be used at room temperature, its activity increases, however, with mounting bath temperature, since with elevated temperatures, the diffusion speed also increases. Temperatures of 10 to 150 C., preferably 30 to C. are used. Through the use of such an intermediate bath there is obtained, not only a homogeneously good metallized product, but also the intermediate rinsing and the activation can be shortened and simplified, since the negative influences of the etching residues are eliminated and the activator can be com pletely developed.

In addition to the already mentioned ethylene diamine solutions of homologous aliphatic diamines and simple substituted diamine of the general formula /N(CH2),N RI R!!! where R, R, R", and R'" are hydrogen, methyl or other lower aliphatic groups (e.g., alkyl up to 6 carbon atoms, or CH COOH or their salts, e.g., ammonium or alkali metal salts) and x is 2 to 8 are useful. Additionally mawhere R, R, R, and R' are the same as defined above and y is 0 to 4 are also very valuable the invention.

Examples of such compounds include propylene diamine, tetramethylene diamine, hexamethylene diamine, octamethylene diamine, N-methyl ethylene diamine, N,N- dimethyl ethylene diamine, N-ethyl hexamethylene diamine, bis (1,4-aminomethyl) cyclohexane, bis (1,4- aminoethyl) cyclohexane, bi's(l,4-aminopropyl)cyclohexane, bis(l,4-aminobutyl) cyclohexane, l,4-di(aminomethyl)-benzene, 1,4- diaminoethyD-benzene, 1,4 di (aminopropyl)-benzene, 1,4-di(aminobutyl-benzene, N- ethylI,4-di(aminobutyl)-benzene, ethylene diamine tetraacetic acid and the mono, di, tri and tetra sodium, ammonium and potassium salts thereof, ethylene diamine triacetic acid and the mono, di and tri sodium, ammonium and potassium salts thereof, ethylene diamine diacetic acid, ethylene diamine monoacetic acid and the sodium, potassium and ammonium salts thereof, trimethylene diamine tetraacetic acid, tetramethylene diamine tetraaoetic acid and its sodium, potassium and ammonium, p-phenylene diamine tetraacetic acid and its sodium, potassium and ammonium salts.

The amines are used preeminently in aqueous solution in an amout of 1 to 80% by weight of the bath liquid, preferably 2 to and most preferably 2 to 8%.

There can also be used, as stated, ammonia or amines such as methyl amine, ethyl amine, butyl amine, dimethyl amine, dipropyl amine, dibutyl amine, trimethyl amine, triethyl amine, tributyl amine, dimethyl propyl amine, or quaternary ammonium compounds, such as tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide, tetrabutyl ammonium hydroxide.

To neutralize the residual acid of the etched plastic samples, there is also added to the solution alkalies, e.g., sodium hydroxide and potassium hydroxide. Preferably there is used at least as much alkali hydroxide as is included in the application reaching chemical metallization bath. Thus, the amine or ammonium compound containing bath can have 0.1 to by Weight of alkali, preferably 0.4 to 8% of sodium hydroxide.

For the connected chemical copper plating with a modified Fehlings solution, the addition of 8 to grams of NaOH per liter of bath solution has proven suitable.

As is made evident by the following examples, this intermediate bath is advantageously used after the etching of the plastic sample and after a short rinsing with water. There can be used with the intermediate bath of the invention either the conventional sensitization of the plastic samples with SnCl solution or also an activation process with a diluted noble metal salt solution, e.g., with 0.1 to 10% by weight, preferably 0.2 to 4% of silver or palladium compounds such as silver nitrate and palladium chloride or other noble metal compounds such as ammoniumchloroplatinate.

In so far as the foregoing sensitization is eliminated in order to be able to reduce the reracking of the plastic parts to unactivated supports, a short treatment in a bath containing a reducing agent suitable for strengthening of the activation should follow by which the activator ions become converted to activator nuclei suitable for the chemical metallization process.

According to a further variation of the process of the invention, by following the metallization processes described in application Ser. No. 593,736 filed Nov. 14, 1966, now abandoned and application Ser. No. 753,780 filed Aug. 19, 1968, now abandoned there can be eliminated both the reducing agent containing preliminary bath before the metallization bath and a corresponding intermediate rinsing with deionized water if there are added to the amine containing decontamination bath noninhibiting acting solutions of metal salts whose redox potentials are more negative than the activation solution employed for the application and which are able at times to form clear soluble complexes with the amines or amine mixtures used. Thus, there can be used baths containing nickel and/or cobalt and/or copper salts in amounts of 0.1 to 10% by weight, preferably 0.2 to 5% of the entire bath liquid. A's examples of such salts there can be used nickel chloride, cobaltous chloride, copper sulfate, nickel sulfate, cobaltous sulfate, zinc chloride, zinc sulfate.

For example, for the metallization of plastics modified with fillers, the etched plastic sample has been treated with an aqueous sodium alkali solution of ethylene diamine and nickel chloride of the following composition which has proven very advantageous:

Grams Ethylene diamine/liter 60 Nickel chloride/liter 30 Caustic soda/liter 40 Water Balance In place of ethylene diamine there can be used with equal effectiveness ethylene diamine tetraacetic acid or its salts, e.g., Complexon III which is Na H [CH N(CH COO) in a bath of the following composition:

Grams Complexon III/liter 47.6 Nickel chloride/liter 30.0 Caustic soda/liter .40 Water Balance Through the use of such metal salt and amine containing intermediate bath the process can be reduced=to the following process steps:

The procedure in this metallization process can still be shortened by two process steps if the activation likewise is incorporated in the intermediate treatment. This is successful if instead of the just mentioned metal salt solution a very dilute noble metal salt solution is added to the amine containing intermediate bath. Thus, for example, for the metallization of plastics modified with fillers solutions of the following composition have proved to be very good:

60 grams ethylene diamine/liter 0.1-2 grams AgNO /liter balance deionized water or 60 grams ethylene diamine/liter 0.2-2 grams PdClg/ liter 40 grams NaOH/liter balance water Through the use of such solutions, the procedure is simplified to the following steps which besides in'time are reduced to the least amount.

(a) chromosulfuric acid etch (b) rinsing with deionized water or tap water (c) afirlnine and noble metal salt containing intermediate (d) short rinsing with deionized water (e) metallization in a chemical metallization bath and the connected conventional plating and improving in electrolytic baths.

The process is primarily very advantageously usefulin the metallization of polypropylene modified with fillers which is additionally superior in heat stability to ABS plastics.

The following table of the collected examples gives a clear view of the metallization results obtainable and the adhesive strength of the metal layer and the extent of the shortening of the total process through the introduction TABLE 2 Example No.-

of the intermediate bath of the invention in various compositions. Unless otherwise indicated, all parts and percentages are by weight.

In the examples, the abbreviation EDA stands for Wor ing conditions ethylene diamine. The aqueous EDA/NaOH decontami- 5 Bath: nation solution contained 60 grams ethylene diamine per liter and 40 grams NaOH per liter.

Example No.-

20 Ml./l. Rinse (deionized water), 20

TABLE 3 (EDA! NaOH/NiClo). Decontamination (EDA/ ized water), seconds.... Preliminary reduction bath minutes.

nized, minutes Decontamination (EDA/ Total treatment time,

minutes Total treatment time,

minutes-- The metal plated samples were then tested for adhesion after electroplating using (a) 40 ,um and (b) 50 ,um (mi- Rinse (deionized wate Minutes..

1 Seconds.

Deio

Minutes-..-

Rinse (deion Minutes-. (ML.

50 Rinse (deionized water),

Example No.--

NaOH),

econtamination N aOH/CoCh) minutes Rinse (deionized water),

seconds Activation, m

. seconds in addition to the amounts of AgNO or PdCl indicated 20 Prelimi ary educt both 40% formalin/NaOh:

seconds Regular chemical copper plating, minutes Working conditions NaOH/NlClr), minutes Decontamination (EDA/ NaOH/OuSOQ, minutes Decontamination plus activator (EDA/AgNOz), minutes.-

Rinse (deionized water),

seconds.......-...-......

Regular chemical copper plating, minutes.-.

cron). The samples were all 3 mm. thick. The results are set forth in Table 4. The adhesion is measured in kg. per 60 inch.

AgNoa/NH g.ll.. Rinse (deionized ter),

Rinse waterz 54 1 LLL2 TABLE 4 LLLL 5 Example No.-

TABLE 1 Sample polymer H2804 (g./1.) Rinse Water deionized, minutes. Neutralization soda lye,

Minutes-.

G./l Rinse in deionized water,

Total treatment time,

minutes.

1 Seconds.

The aqueous EDA/NaOH/NiCl decontamination solution contained 60 grams ethylene diamine/ liter, grams NaOH/liter and 30 grams NiCI /Iiter.

The aqueous EDA/NaOH/CoCl decontamination solution contained grams ethylene diamine/liter, 40 grams NaOH/ liter and 30 grams CoCl /liter.

The aqueous solution of decontaminant and activator contained 60 grams ethylene diamine/liter and 0.2 gram 15 AgNO liter.

The aqueous sensitization solution contained 10 grams of SnCl liter and 25 grams of HCl/ liter.

The activator solution contained 3 grams of NH /liter The reduction preliminary bath contained 7 grams/liter of NaOH in addition to the indicated amount of formalin or NaBH The time in the etching bath was 10 minutes for all 25 samples except those with 20% filler. The samples with 20% filler were kept in the etching bath 2 0 minutes.

The polypropylene samples were composed of 55% polypropylene, 15% ethylene-vinylacetate copolymer and All temperatures are in degrees Centigrade.

minutes.. Decontamination (25% NlEhOH), minutes.

Rinse in deionized Water,

minutes- Sensitization (SIlClzHCi) minutes Rinse, deionized water,

minutes Activation AgNOa/NHzI minutes Regular chemical copper plating, mlnutes ABS samples were 100% acrylonitrilebutadiene-styrene copolymer.

in the table.

30% SiO The polyethylene sample was composed of 30 polyethylene, 15 ethylene-vinylacetate copolymer and 20% CaSiO The polyvinyl chloride sample was composed of polyvinyl chloride and 20% SiO The 1 Polypropylene 2 Polyethylcne 3 Polyvinyl chloride.

4 ABS 5 H m H d n 0 c g m: am We.

What is claimed is:

1. In a process for the adhesive metallization of plastics including pretreating of the plastic surface with chromosulfuric acid to etch said surface and subsequent chemical metalliaztion from an aqueous metal salt bath and electroplating, the improvement comprising after the chromosulfuric acid etch, treating at 10 to 150 C. said plastic surface in an alkaline aqueous solution of ethylene diamine as an intermediate bath as a neutralizing agent and to bind metal ions coming from the etching, said solution containing 1 to 80% of the ethylene diamine, 0.1 to 30% of alkali and 0.1 to 10% of a member of the group consisting of nickel, cobalt, copper, silver, palladium and platinum salts.

2. A process according to claim 1 wherein the ethylene 1 diamine bath contains from 0.1 to 10% of a nickel, cobalt or copper salt based on the entire bath weight.

3. A process according to claim 1 wherein the diamine bath includes a silver or palladium salt in an amount of 0.1 to 10%.

4. A process according to claim 1 wherein the plastic is selected from the group consisting of polypropylene, polyethylene, polyvinyl chloride and acrylonitrilebutadiene-styrene copolymer.

References Cited UNITED STATES PATENTS OTHER REFERENCES Kirk-Othmer Encyclopedia of Chem. Tech. (1965), pp.

5 22 thru 25 of vol. 7 cited.

US. Cl. X.R. 

